334 SEWAGE AND ITS PURIFICATION 



of an effluent from a works producing nitro-naphthalene. 

 When diluted by cooling and condenser water, it was apparently 

 harmless to fish under the conditions at the point of discharge. 

 On investigation of the mud near the outfall, however, it was 

 found to have a strong smell of naphthalene products, and all 

 signs of the organic life, necessary for the gradual breaking 

 down of putrefactive matter, had disappeared. This effect was 

 discernable 400 metres below the outfall. In a recent case of 

 alleged contamination from a paper-mill I found a considerable 

 amount of gypsum, chalk and various pigments in the river 

 mud. In another instance, below a copper w^orks, although 

 the water appeared to be free from dissolved copper, the metal 

 was present in the mud, and had an injurious effect on fish. 



Especially in the North of England, processes for treatment 

 of factory waste-waters on the works themselves have been 

 greatly improved, and in a large number of cases made 

 remunerative by recovery of products. Mr. Tatton, inspector 

 of the Mersey and Irwell Board, classifies these liquors into 

 those from (i) print works, (2) dye works, (3) bleach works, 

 (4) waste bleach works, (5) paper-mills, (6) paper stainers, 

 (7) tanners and leather dressers, (8) fellmongers, (9) woollen 

 trades, (10) silk trades, (11) coal slack washers, (12) soap- 

 makers, (13) stone polishers, (14) chemical manufacturers, 

 (15) brewers, (16) unclassified.^ The discharges are mostly 

 dealt with, after screening, by precipitation with iron and lime, 

 and as mentioned in Chapter VII., a ferric salt is found to be 

 more effective than a ferrous salt (copperas). 



Bleach y Dye, Finishing and Calico-printing Works. — The waste 

 liquors contain various dyes and mordants, soap, starch, soda 

 or acids, exhausted bleach, etc. They are generally screened 

 and settled, and in some works traverse a long channel in 

 which blocks of iron alum (ferric ammonium sulphate) are 

 suspended and gradually dissolve, precipitating most of the 

 colouring and other matters. Lime is added either before or 

 after the iron precipitation, in various amounts according to 

 quality of the liquids. After again settling in tanks, the liquid 

 is usually drawn off by floating outlets and passed through 

 shallow (i|- to 3J ft.) graded filters of stones and clinkers 

 covered with 6 to 18 in. of fine ashes, which are renewed at 

 intervals. Owing to biological action and the formation of 



1 " Purification of Water after Use in Manufactories," by R. A. Tatton, 

 M.I.C.E. , Proc. Inst. Civ. Engineers, Jan. 9, igoo. 



